1. Field of the Invention
The present invention relates to a plasma display panel (PDP) used such as for a display device, and to a PDP production method.
2. Description of the Prior Art
A plasma display panel (PDP) has recently received much attention as a flat panel display used in computers and televisions.
A PDP is classified as one of two major types, namely a DC-type and an AC-type, of which the latter has become mainstream because it is suitable for use in a large display.
To illuminate discharge cells of an AC-type PDP, an AC pulse voltage is applied to electrodes covered by a dielectric layer that sustains a discharge. With an AC-type PDP, a surface-discharge type and an opposed-discharge type are widely known. For the surface-discharge type, pairs of sustained electrodes are placed in parallel on a front panel. For the opposed-discharge type, pairs of sustained electrodes are placed on both the front panel and the back panel, and so the pairs of sustained electrodes face one another.
FIG. 10 shows a standard AC surface-discharge PDP as one example.
For this PDP, a front panel 110 and a back panel 120 face each other, and outer parts (not shown in the figure) of their facing surfaces are bonded with a sealing material made of low-melting glass.
For the front panel 110, pairs 112a-112b of display electrodes are formed on a front substrate 111 on a side facing the back panel 120. A dielectric layer 113 made of dielectric glass, and a protecting layer 114 made of magnesium oxide (MgO) cover the display electrode pairs 112a and 112b. 
For the back panel 120, address electrodes 122 are formed in parallel at certain intervals on a back substrate 121 on a side facing the front panel 110. A back dielectric layer 123 covers the address electrodes 122, and partitions 130 are formed in parallel at certain intervals on the back dielectric layer 123 along the address electrodes 122. Phosphor layers 140 for respective colors (red, green, and blue) are formed in channels between the partitions 130.
With the above construction, the display electrode pairs 112a and 112b are placed perpendicular to the address electrodes 122. At intersections of the display electrode pairs 112a-112b and the address electrodes 122, discharge cells are formed.
Based on image data to be displayed, an address pulse voltage is first placed between the address electrodes 122 and the display electrode pair 112a. After this, a sustain pulse voltage is placed between the display electrode pair 112a and 112b. This causes a sustained discharge to occur selectively in the discharge cells, so that ultraviolet rays are emitted from the discharge cells where the sustained discharge occurs. The emitted ultraviolet rays excite the RGB phosphor layers 140, which then emit visible light, so that images are displayed on the PDP.
Adjacent discharge cells are separated by the partitions 130, which prevent a crosstalk phenomenon, i.e., a state in which discharges at different discharge cells mix, from occurring.
The partitions 130 are usually produced by having a partition material such as a glass material formed into a partition pattern (i.e., stripes) and baking the formed partition material at a temperature higher than a softening point of the glass material contained in the partition material. There are three major partition forming methods as follows. The first one is called a xe2x80x9cprinting methodxe2x80x9d, with which a partition pattern is printed using a paste containing the partition material, such as by the screen printing. The second method is called a xe2x80x9csandblasting methodxe2x80x9d. For this method, the above paste is applied onto the entire surface of the back substrate, and then a photosensitive film layer is formed on this paste. The predetermined partition pattern is then formed using photography. After this, unnecessary paste is removed by sandblasting. The third method is called a xe2x80x9cphoto-paste methodxe2x80x9d. In this method, a photosensitive paste containing the partition material is applied onto the entire surface of the back substrate, and then unnecessary portions are removed using photography.
When a partition material is formed into a partition pattern using any of the above three partition forming methods and then baked, an end part 130a of a resulting partition 130 swells and becomes higher than other parts, such as a part 130a. When compared with the part 130b, this end part 130a becomes high by ten to twenty percent.
A swelling such as in the end part 130a is likely to be generated especially when the partitions 130 are formed on the back dielectric layer 123 on the back substrate 121.
The swellings in the end parts of the partitions 130, however, make it difficult to join a back substrate and a front substrate together without leaving any gaps between the partitions 130 and the front substrate during an assembly of a PDP. When this PDP with gaps is driven, an improper discharge or an abnormal discharge is likely to occur in adjacent cells. In addition, due to the above gaps, the front panel vibrates, so that noise is likely to be generated.
The present invention is therefore made in view of the above problems, and aims to provide a technique for easily producing partitions whose end parts do not swell, thereby providing a PDP capable of displaying a high-quality image.
To solve the above problems, the partitions of a PDP according to the present invention include a plurality of main parts that extend parallel to either first electrodes or second electrodes. Each main part contains an end part and a central part, and the end part is wider than the central part.
When the above partitions are baked, no swellings are produced in their end parts.
Note that for forming a partition patter, standard processes such as the xe2x80x9csandblasting methodxe2x80x9d and the screen printing method can be used.
The following describes reasons why the partitions of the present invention prevent swellings from being produced in the end parts of the partitions.
Usually, a partition material tries to contract during baking, so that large tension is exerted parallel to the longitudinal direction of main parts. A central part of a main part is pulled toward two opposite directions that are parallel to the longitudinal direction of the main part. On the other hand, an end part of the main part is pulled toward the center, but not pulled toward the direction opposite to the center.
A swelling is therefore considered to be produced when the partition material making up a portion near the surface of the end part moves due to the pulling force exerted to the end part toward the center.
When a main part has an end part that is wider than a central part, the pulling force is distributed over the wide end part so that the movement of the partition material can be suppressed. Moreover, when the end part of the main part extends parallel to the direction of the main part""s width in this way, tension is exerted parallel to the width direction as well as toward the center. This tension parallel to the width direction is also considered to suppress swellings.
To make a width of the end part larger than that of the central part, the end part may have a shape whose cross section is similar to either a letter xe2x80x9cTxe2x80x9d or a letter xe2x80x9cLxe2x80x9d.
In order to allow each partition to have ends that are wider than a center of the partition, a sub part is provided to each main part for the present invention. This sub part extends from an end part of the main part parallel to a direction of a width of the main part.
When end parts of every two adjacent main parts are connected with one another by such a sub part, large tension is exerted parallel to the direction in which the sub part extends. This construction is effective in suppressing swellings in the end parts.
It is desirable that a sub part has a larger width than a main part, preferably at least 1.5 times as large as a main part, so as to have sufficiently large tension exerted parallel to the direction in which sub parts extend. However, when end parts of all the main parts are connected with one another by sub parts, the above sufficiently large tension can be still exerted even if sub parts have a narrower width than main parts.
Also with the present invention, end parts of partitions are partially heated, after the partitions are baked, to a temperature higher than a softening point of a partition material during the partition forming process. As a result, when the end parts swell after the baking process, the swellings can be reduced by the partial heating process for reasons described below.
When an end part is partially softened by the heating and then solidifies, surface tension is exerted to this end part. As a result, the partition material making up a swelling in the end part disperses to its periphery.
As a specific partial heating method, a method with which a laser beam is projected onto an end part of each partition is suitable.
For the reasons described above, the present invention can suppress swellings produced in end parts of partitions of a PDP. As a result, a gap is not likely to be produced between the partitions and a substrate facing the partitions. This prevents an improper discharge and an abnormal discharge from occurring in adjacent cells during driving of the PDP. In addition, vibration of a substrate during the driving can be prevented.